In current industrial practice, known porous silicocalcareous masses are made from a thorough mixture of lime, ground silica or fossil silica and asbestos suspended in water. The resulting paste introduced into containers, molds or bottles, is then subjected to heat in an autoclave to initiate and complete the lime-silica reaction which gives rise to the silicocalcareous material; then it is transferred to a drying furnace to remove the water and create the desired porosity.
Asbestos is added to the aqueous composition of silica and lime for its effect as a reinforcing fiber and suspension agent. However, recent constraints related to health and safety connected with the handling of asbestos have led to reconsideration of the use of this natural fiber whose characteristic properties, in the manufacture of porous silicocalcareous masses, are useful in strengthening the crystalline structure and contributing to the maintenance of the suspension of the solid products, silica and lime, in a large amount of water.
It is known that the stabilization of the suspension can be markedly improved by the use of suspension agents. USP 3,406,030 discloses the effect of adding substantial amounts of organic agents, up to 10%, for suspension purposes. Certain cellulose derivatives such as alkylhydroxyalkylcelluloses, in particular methyl and ethylhydroxyethylcelluloses, make it possible to obtain an excellent stabilization of the suspension. The dose to be introduced varies with the degree of stabilization sought and the nature of the suspension agent.
Compensating for the discontinuance of asbestos by adding organic suspension agents in large amounts has been considered. While it has been shown that the addition of an organic suspension agent in a large amount can appreciably correct the defect of decanting the solid products during the manufacture of the silica/lime and water paste, on the other hand, due to the fact of the destruction of this type of organic compound during the firing of the paste, a lowering of the mechanical properties of the dried silicocalcareous masses with high porosity has been noted. The fragility and friability of the porous materials thus obtained are such that they render them unsuitable for the applications concerned.